Process for radioisotope recovery and system for implementing same

ABSTRACT

A method of recovering daughter isotopes from a radioisotope mixture. The method comprises providing a radioisotope mixture solution comprising at least one parent isotope. The at least one parent isotope is extracted into an organic phase, which comprises an extractant and a solvent. The organic phase is substantially continuously contacted with an aqueous phase to extract at least one daughter isotope into the aqueous phase. The aqueous phase is separated from the organic phase, such as by using an annular centrifugal contactor. The at least one daughter isotope is purified from the aqueous phase, such as by ion exchange chromatography or extraction chromatography. The at least one daughter isotope may include actinium-225, radium-225, bismuth-213, or mixtures thereof. A liquid-liquid extraction system for recovering at least one daughter isotope from a source material is also disclosed.

GOVERNMENT RIGHTS

The United States Government has rights in the following inventionpursuant to Contract No. DE-AC07-99ID13727 between the U.S. Departmentof Energy and Bechtel BWXT Idaho, LLC.

FIELD OF THE INVENTION

The present invention relates to a method of recovering radioisotopes.More specifically, the present invention relates to an extraction methodfor recovering radioisotopes from breeder reactor fuel.

BACKGROUND OF THE INVENTION

In the medical field, numerous radioisotopes are used for diagnosticsand for treating various forms of cancer. Radioisotopes that are capableof emitting alpha particles, such as radium-223, actinium-225(“Ac-225”), and bismuth-213 (“Bi-213”), are particularly advantageous intreating cancers because they provide highly ionizing radiation thatdoes not penetrate far from the radioisotope. If the alpha emitter isplaced near a tumor site or cancer cell, its effects are localized tothose sites without significantly affecting healthy, surrounding tissue.For instance, Bi-213 decays via a daughter isotope, polonium-213(“Po-213”), producing alpha emissions that have an extremely high energyof about 8.4 MeV. Research and clinical trials for using Bi-213 labeledmonoclonal antibodies as cancer therapy tools have been ongoing for atleast a decade. While alpha emitters have shown effectiveness intreating cancers, these radioisotopes are often generated in smallquantities and must be separated from other radioisotopes that arepresent in source materials.

One potential source of Bi-213 is from Ac-225, which is a decay productof thorium-229 (“Th-229”). Th-229 is a daughter isotope of uranium-233(“U-233”), stockpiles of which remain from nuclear power plant reactorsand nuclear weapons programs. However, in order to generate sufficientquantities of the Bi-213, the Ac-225 and Bi-213 must be easily,economically, and safely removed from other radioisotopes andnon-isotope impurities in the U-233 stockpiles. For instance, the Ac-225must be easily separated from Th-229 and U-233. However, the nuclearstockpiles at various nuclear storage facilities in the United States,such as Oak Ridge National Laboratory (“ORNL”) or Idaho NationalEngineering and Environmental Laboratory (“INEEL”), are composed ofdifferent radioisotopes or matrices. Therefore, different separationmethods are needed to separate and purify the Ac-225 and Bi-213 fromeach of the different nuclear stockpiles.

Various methods, such as precipitation or chromatographic methods, havebeen disclosed to isolate Ac-225 and Bi-213 from radioactive sourcematerials. In published United States Patent Application No. 20040052705to Tranter et al. (“Tranter”), which is assigned to the same assignee asthe present invention, a precipitation process for recovering anAc-225/Bi-213 product from a thorium source material is disclosed. Asolution that includes a first volume of nitric acid and at least someof the thorium source material is provided. Iodate is added to thesolution and at least some of the iodate combines with the thorium toform a thorium iodate precipitate. A supernatant containing at leastsome of the first volume of nitric acid is separated from the thoriumiodate precipitate and a second volume of nitric acid is added to thethorium iodate precipitate. The precipitate is stored in the secondvolume of nitric acid for a generation time period during which athorium-229 decay product comprising Ac-225 and Bi-213 is generated. Thesecond volume of nitric acid containing at least some of the Th-229decay product is separated from the thorium iodate precipitate and isfiltered to remove at least some of any residual thorium iodateprecipitate present. After filtering, the second volume of nitric acidis treated using at least one chromatographic procedure to separateAc-225 and Bi-213 from at least some of any impurities that are presentin the second volume of nitric acid.

In published Unite States Patent Application No. 20040062695 to Horwitzet al., the disclosure of which is incorporated by reference herein, aseparation medium having a diglycolamide (“DGA”) extractant dispersedonto an inert, porous support is disclosed. The separation medium isused to selectively extract multivalent cations, such as scandium(III),yttrium(III), lanthanum(I), actinium(III), trivalent americium,trivalent yttrium, and trivalent ytterbium, from an acidic, aqueoussolution.

In U.S. Pat. No. 5,854,968 to Horwitz et al., the disclosure of which isincorporated by reference herein, Bi-213 cations are isolatedchromatographically from an aqueous feed solution produced from thedecay products of U-233. To isolate the Bi-213, Ac-225 is first isolatedfrom the aqueous feed solution by ion exchange chromatography. Theaqueous feed solution is contacted with a first ion exchange medium toseparate the Ac-225 from the aqueous feed solution. The first ionexchange medium is a TEVA™ resin, which is a tetravalent actinide resinhaving a quaternary ammonium salt sorbed on a water-insoluble support. Asolution having the Ac-225 is then exposed to a second ion exchangemedium to bind the Ac-225. The second ion exchange medium includesdiphosphonic acid (“DPA”) groups sorbed onto an inert substrate and isknown as Dipex®. The second ion exchange medium, having the boundAc-225, is maintained for a sufficient amount of time for the Ac-225 todecay to Bi-213, which is then eluted from the second ion exchangemedium.

In published United States Patent Application Publication 2003/0194364to Bond et al., a multicolumn method of obtaining purified Ac-225 isdisclosed. The Ac-225 is separated from a thorium source material usinga primary separation column. The primary separation column is a strongacid cation exchange resin. The Ac-225 is retained by the primaryseparation column while the thorium elutes. The Ac-225 is removed fromthe primary separation column and passed through a guard column. Theguard column is a UTEV® or UTEVA®-2 resin, a TEVA resin, an anionexchange resin, or 2-ethylhexyl-2-ethylhexylphosphonic acid on an inertsubstrate. The guard column retains additional amounts of thorium thatare present while the Ac-225 elutes.

U.S. Pat. No. 5,809,394 to Bray et al. discloses a method of removingplutonium, cobalt, copper, lead, or other cationic impurities from amixture of radionuclides, such as actinium-227 or thorium-229. Thecationic impurities are removed by acidifying the mixture, oxidizing themixture, and passing the oxidized mixture through an anion exchangecolumn. The purified radionuclides are used as a source for alphaemitters, such as radium-223 and Ac-225.

Liquid-liquid extraction methods for extracting uranium and thorium arealso known in the art. For instance, the Acid-Thorex process is known toseparate thorium and U-233. The Acid-Thorex process utilizes n-tributylphosphate (“TBP”) in normal paraffin hydrocarbon as the extractant. InMason et al., Chapter 7, “Demonstration of the Potential for DesigningExtractants with Preselected Extraction Properties: Possible Applicationto Reactor Fuel Reprocessing,” ACS Symposium Series #117, AmericanChemical Society, Washington, D.C., p. 89–98 (1980), a liquid-liquidextraction method of separating U(VI) and Th(IV) is disclosed. Theliquid-liquid extraction uses neutral or monoacidic, phosphorus-basedorganic compounds as the extractants. In Benedict, Chapter 26,“Improvements in Thorium-Uranium Separation in the Acid-Thorex Process,”ACS Symposium Series #117, American Chemical Society, Washington, D.C.,p. 371–377 (1980), dibutyl phosphate (“DBP”) and low concentrations offluoride ions are disclosed for use with the Acid-Thorex process. InGrant et al., Chapter 25, “Heavy Element Separation forThorium-Uranium-Plutonium Fuels,” ACS Symposium Series #117, AmericanChemical Society, Washington, D.C., p. 351–369 (1980), TBP is used toseparate Th, U-233, and plutonium from one another using a modifiedThorex solvent extraction that includes 30% TBP.

Chromatographic methods have also been used to separate uranium fromacidic media. In Dietz et al., “An improved extraction chromatographicresin for the separation of uranium from acidic nitrate media” Talanta54:1173–1184 (2001), an extraction chromatographic resin is disclosed toselectively retain U(VI) over other cations, such as Fe(III), fromnuclear waste samples. The extraction chromatographic resin contains aliquid stationary phase that includes an equimolar mixture ofdi-n-amyl-n-amylphosphonate (“DA[AP]”) and a trialkylphosphine oxide(“TRPO”) sorbed onto silanized silica.

ORNL currently supplies Ac-225 as a source material for Bi-213 labeledmonoclonal antibodies. It is believed that the Ac-225 is obtained fromORNL's uranium supply, which is pure uranium, by dissolving the U-233and daughter isotope Th-229 and separating the Th-229 from the U-233.ORNL's U-233 supply is approximately 40 years old and, therefore,contains a useful quantity of Th-229, about 40 grams, which subsequentlydecays into the Ac-225. However, since the half-life of U-233 is1,580,000 years, only small amounts of Th-229 are generated by the decayof U-233. The Th-229 is separated from the U-233 by ion exchangechromatography. The Th-229 is retained on the ion exchange column. Afterthe Th-229 decays to Ac-225, the Ac-225 is eluted from the ion exchangecolumn, collected, and shipped to a customer. However, this method andquantity of parent isotopes is unable to produce sufficient amounts ofAc-225 to satisfy the current need in clinical trials.

It would be desirable to provide a method of producing alpha emitters,such as Ac-225 and Bi-213, in sufficient amounts to meet current demandsfor cancer therapies. In addition, it would be desirable to utilizeadditional unused nuclear materials, which are currently classified asnuclear waste, for research, medical diagnostics and medical treatments,including immunotherapy.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a method of recovering at least onedaughter isotope from a radioisotope mixture. The method comprisesproviding a radioisotope mixture solution comprising at least one parentisotope. The radioisotope mixture solution may be formulated as anaqueous, acidic solution that comprises uranium and thorium. In oneembodiment, the acidic solution may have a nitric acid concentrationranging from approximately 2 M to approximately 6 M. The radioisotopemixture solution may comprise at least one of uranium-232, uranium-233,thorium-228, thorium-229, thorium-232, and mixtures thereof. The atleast one parent isotope may be extracted into an organic phase, whichcomprises an extractant selected from the group consisting of n-tributylphosphate, dibutyl phosphate,di-n-amyl-n-amylphosphonate(di-n-pentyl-n-pentylphosphonate), dibutylbutyl phosphonate, butyl dibutyl phosphinate, dibutyl cyclohexylphosphonate, dibutyl chloromethyl phosphonate,tri(4-methylpentyl-2)phosphate, butyl phosphonate,di(4-methylpentyl-2)butyl phosphonate, di(4-methylpentyl-2)isobutylphosphonate, di(4-methylpentyl-2)propyl phosphonate, anddi(2-ethylbutyl)2-ethylbutyl phosphonate. The organic phase may alsocomprise a diluent selected from the group consisting of benzene, carbontetrachloride, isopropyl ether, 1-octanol, 2-ethyl hexanol, 1-decanol,1-octanoic acid, methyl isobutylketone, p-diisopropylbenzene, dodecane,n-heptane, kerosene, a normal paraffinic hydrocarbon solvent, and anisoparaffinic hydrocarbon solvent.

The organic phase comprising the extracted, at least one parent isotopemay then be substantially continuously contacted with an aqueous phase,which may include from approximately 2 M to approximately 6 M nitricacid. At least one daughter isotope is extracted into the aqueous phaseand the organic phase is separated from the aqueous phase. The organicphase and the aqueous phase may be continuously contacted, extracted,and separated using an annular centrifugal contactor. The at least onedaughter isotope is purified from the aqueous phase, such as by ionexchange chromatography or extraction chromatography. To purify the atleast one daughter isotope, tramp organics may be removed from theaqueous phase by extracting the tramp organics with an immisciblealcohol. In one embodiment, actinium-225 is sorbed onto a diglycolamideresin, wherein the diglycolamide resin comprises atetraalkyldiglycolamide extractant coated onto inert support particles.The at least one daughter isotope may be Ac-225, Bi-213, Ra-225, ormixtures thereof. The purified daughter isotopes may be allowed to decayto produce subsequent daughter isotopes.

The present invention also relates to a liquid-liquid extraction systemfor recovering at least one daughter isotope from a radioisotopemixture. The liquid-liquid extraction system comprises a first vesselconfigured to separate an organic phase from a first aqueous phase forextraction of at least one parent isotope, such as uranium or thorium,from the first aqueous phase into the organic phase. A second vessel maybe operatively coupled to the first vessel to receive the organic phaseincluding the extracted at least one parent isotope therefrom and isconfigured to substantially continuously contact the organic phase witha second aqueous phase to extract at least one daughter isotope from theorganic phase into the second aqueous phase and separate the organicphase from the second aqueous phase including the extracted at least onedaughter isotope. The first vessel and the second vessel may eachcomprise an annular centrifugal contactor. A separation columnconfigured to purify the at least one daughter isotope from the secondaqueous phase may be operatively coupled to the second vessel to purifythe at least one daughter isotope from the second aqueous phase. The atleast one daughter isotope may be Ac-225, Bi-213, Ra-225, or mixturesthereof.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention may be more readily ascertained fromthe following description of the invention when read in conjunction withthe accompanying drawings in which:

FIG. 1 shows a radioactive decay chain of U-233 to Bi-209. Half-lives ofthe radioisotopes are indicated in years (y), days (d), hours (h),minutes (m), seconds (s), or milliseconds (ms);

FIGS. 2 and 3 are block diagrams illustrating embodiments of systems andmethods of recovering Ac-225 according to the present invention;

FIG. 4 is a schematic illustration of an annular centrifugal contactor(“ACC”); and

FIG. 5 is a block diagram illustrating an embodiment of a system andmethod of recovering Ac-225 according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A method of recovering at least one daughter isotope of interest from amixture of radioisotopes is disclosed. The daughter isotope of interestmay be at least one of Ac-225, Bi-213, radium-225 (“Ra-225”), andmixtures thereof. The radioisotope mixture may include two or moreradioisotopes, with at least one of the radioisotopes being a parentisotope. As used herein, the term “parent isotope” refers to aradioisotope that is capable of undergoing radioactive decay to thedaughter isotope of interest. For the sake of example only, the parentisotope is U or Th. As used herein, the term “daughter isotope” refersto a first or subsequent decay product isotope that is generated fromthe parent isotope. As such, the term “daughter isotope” alsoencompasses a subsequent decay product generated from a first decayproduct isotope.

The radioisotope mixture may be a breeder reactor fuel that includes,but is not limited to, U-233, U-232, Th-228, Th-229, Th-232, andmixtures thereof. The radioisotope mixture may also include Ac-225. AU-233 stockpile in the form of unirradiated Th-232/U-233 breeder reactorfuel is currently stored at the INEEL. Fresh breeder reactor fuel mayinclude a small amount of U-233 that is required to go critical orsustain a fission process. The fresh breeder reactor fuel may includeapproximately 3% U-233 and approximately 97% Th-232. The Th-232 ispresent in the breeder reactor fuel as a target for neutron capture toproduce more U-233. Since Th-229 decays from U-233, the Th-229 isdiluted into a large mass of Th-232, which may only be separated byisotopic enrichment methods and not by chemical methods. The breederreactor fuel at the INEEL is about 40 years old and, therefore, mayinclude approximately 40 grams of Th-229. Irradiated light water breederreactor (“LWBR”) fuel, which includes Th-229, may also be used as theradioisotope mixture. Since the LWBR fuel includes fission products, theLWBR fuel may first be processed in a facility that is sufficientlyshielded to produce an organic phase loaded with the parent isotopes,which is then further processed as described below.

In the unirradiated breeder reactor fuel, radioisotopes of the U and theTh are the parent isotopes while radioisotopes of Ac and Bi are thedaughter isotopes. As shown in FIG. 1, U-233 decays to Th-229, whichsubsequently decays to daughter isotopes that include Ac-225 and Bi-213.Bi-213 is an alpha and beta emitter that has a half-life ofapproximately 46 minutes. A Bi-213 daughter isotope, Po-213, rapidlyundergoes further alpha decay to form lead-209, which further betadecays to form bismuth-209 (“Bi-209”). Bi-209 is a stable radioisotopeand, therefore, Bi-213 is a highly desired radioisotope for use intreating cancers. Since approximately 13,000 kg of the unirradiatedbreeder reactor fuel described above is currently stored at the INEEL,an adequate supply of the U parent isotopes is available to generatesufficient amounts of Ac-225 and Bi-213. The radioisotope mixture isstably stored at the INEEL in an oxide form as U/Th oxide fuel pellets.The U/Th oxide fuel pellets are present in a variety of pellet sizes,such as pellets having a length of about 0.5 inches and a diameter ofabout 0.5 inches.

Since the radioisotope mixture is present in a solid form, theradioisotope mixture may be dissolved in an acidic solution, forming anaqueous solution of the radioisotope mixture. The radioisotope mixturesolution, in which the parent isotopes are dissolved, may have a nitricacid concentration ranging from approximately 2M to approximately 6M,such as from approximately 3M to approximately 5M. In one embodiment,the nitric acid concentration of the radioisotope mixture solution isapproximately 3M. The nitric acid concentration of the radioisotopemixture solution may be adjusted to maximize extraction of the parentisotopes present in the radioisotope mixture solution into an organicphase, as described in detail below. The radioisotope mixture solutionmay also include a catalyst, such as hydrofluoric acid, to increase thedissolution rate of the radioisotope mixture. The catalyst may bepresent in the radioisotope mixture solution from approximately 0.01M toapproximately 0.05M. To complex any free fluoride that is present afterdissolving the radioisotope mixture, aluminum or boron may also bepresent in the radioisotope mixture solution.

The radioisotope mixture solution may be intermittently or continuallymixed to increase the dissolution of the radioisotope mixture. Duringdissolution, the radioisotope mixture solution may be maintained at atemperature ranging from approximately ambient temperature (25° C.) toapproximately 300° C., such as from approximately 100° C. toapproximately 175° C. In one embodiment, the radioisotope mixture issubstantially dissolved in the acidic solution. However, it is alsocontemplated that the radioisotope mixture solution may be treated, suchas by filtering, to remove any of the radioisotope mixture that is notcompletely dissolved in the acidic solution.

After dissolving the radioisotope mixture, the radioisotope mixturesolution may be subjected to a liquid-liquid extraction in a firstvessel 4, as shown in FIG. 2. The volume of the radioisotope mixturesolution may be extracted in the first vessel 4 at one time or theradioisotope mixture solution may be extracted in a batchwise fashion.The first vessel 4 may be a centrifugal separator or an annularcentrifugal contactor (“ACC”), which is described in detail below. Aliquid-liquid extraction system 12 used to extract the radioisotopemixture solution may include an organic phase 6 and a first aqueousphase 2 having the radioisotope mixture solution. During theliquid-liquid extraction, non-isotope impurities, daughter isotopes, andminor amounts of the parent isotopes may remain in the first aqueousphase 2 while a substantial portion of the parent isotopes may beextracted into the organic phase 6. In other words, after theextraction, organic phase 6′ is enriched in the parent isotopes whilethe first aqueous phase 2′ is depleted in the parent isotopes. Theorganic phase 6′ and the first aqueous phase 2′ may be separated fromone another, as described in detail below. The first aqueous phase 2′may be further processed, such as by additional liquid-liquidextractions, to extract the remaining trace amounts of the parentisotopes, which are combined with the parent isotopes present in theorganic phase 6, or to recover, isolate, and further purify the daughterisotopes of interest, such as Ac-225. The organic phase 6′, which isloaded with the parent isotopes, may be subjected to an additionalliquid-liquid extraction in a second vessel 8. The organic phase 6′ maybe transferred from a storage tank 40 (shown in FIG. 3) to the secondvessel 8. The organic phase 6′ may be substantially continuouslycontacted with at least one additional aqueous phase, such as secondaqueous phase 14, to extract the daughter isotopes of interest 16 thatare produced during radioactive decay of the parent isotopes. Theorganic phase 6′ and the second aqueous phase 14′, which is enriched inthe daughter isotopes of interest 16, may then be separated to isolatethe daughter isotopes of interest 16. The daughter isotopes of interest16 may be continuously extracted from the organic phase 6′ bysubstantially continuously contacting the organic phase 6′ with thesecond aqueous phase 14. The daughter isotopes of interest 16 in thesecond aqueous phase 14′ may then be recovered by chromatographictechniques. In one embodiment, the daughter isotopes of interest 16 areAc-225, Bi-213, Ra-225, and mixtures thereof.

The organic phase 6 of the liquid-liquid extraction system 12 mayinclude a solvent in which an extractant is diluted. The solvent used inthe organic phase 6 may be a diluent, such as benzene, carbontetrachloride, isopropyl ether, 1-octanol, 2-ethyl hexanol, 1-decanol,1-octanoic acid, methyl isobutylketone, p-diisopropylbenzene, dodecane,n-heptane, kerosene, or a paraffinic or isoparaffinic hydrocarbonsolvent, such as Isopar®L or Isopar®M. Isopar®L includes a mixture ofC₁₀–C₁₂ isoparaffinic hydrocarbons and is available from Exxon ChemicalCo. (Houston, Tex.). Isopar®M includes a mixture of isoparaffinichydrocarbons and is available from Exxon Chemical Co. (Houston, Tex.).In one embodiment, the solvent is kerosene. In another embodiment, thesolvent is Isopar®L. The extractant may be selected so that the parentisotope has a high extraction distribution into the organic phase 6. Theextractant may be a neutral or monoacidic organophosphorus typeextractant including, but not limited to, n-tributyl phosphate (“TBP”),dibutyl phosphate, di-n-amyl-n-amylphosphonate (“DA[AP]”), dibutyl butylphosphonate (“DB[BP]”), butyl dibutyl phosphinate, dibutyl cyclohexylphosphonate, dibutyl chloromethyl phosphonate,tri(4-methylpentyl-2)phosphate, butyl phosphonate,di(4-methylpentyl-2)butyl phosphonate, di(4-methylpentyl-2)isobutylphosphonate, di(4-methylpentyl-2)propyl phosphonate, anddi(2-ethylbutyl)2-ethylbutyl phosphonate. Other extractants, as known inthe art, may also be used. The extractant may be present in the organicphase 6 from approximately 0.5 M to approximately 2.0 M. In oneembodiment, the extractant is DA[AP] and is present in the organic phase6 at approximately 1.0M.

The first aqueous phase 2 may include the radioisotope mixture solution,in which the radioisotope mixture is dissolved in the acidic solution.The first aqueous phase 2 may have a nitric acid concentration rangingfrom approximately 2M to approximately 6M, such as from approximately 3Mto approximately 5M.

When the organic phase 6 and the first aqueous phase 2 are combined, theparent isotopes may be extracted into the organic phase 6 of theliquid-liquid extraction system 12 with good efficiency. In other words,the parent isotopes may have high extraction distributions into theorganic phase 6. For instance, the forward extraction distributions ofU-233 and Th-229 into 1M DA[AP] in kerosene from 2M nitric acid are 295and 70.5, respectively. As used herein the terms “forward extract,”“forward extracted,” or “forward extraction” refer to removing orextracting the U-233 and Th-229 from the first aqueous phase 2 into theorganic phase 6. Extraction distributions or distribution coefficientsmay be calculated as known in the art. A higher distribution coefficientindicates a higher removal efficiency for the ion. At a higher nitricacid concentration, such as at 3M nitric acid, the forward extractiondistributions may be slightly higher. Conversely, the daughter isotopesof interest 16 may have low extraction distributions in the organicphase 6, such as less than 0.1. The first aqueous phase 2 may beextracted with the organic phase 6 until a sufficient loading of theparent isotopes is obtained in the organic phase 6′. Extraction of theorganic phase 6 with the first aqueous phase 2 may be performed for fromapproximately 8 hours to approximately 10 hours to obtain the sufficientloading.

The organic phase 6′, which is enriched in the parent isotopes, may thenbe transferred to the second vessel 8. Over time, the parent isotopesmay decay into daughter isotopes, including the daughter isotopes ofinterest 16. To isolate the daughter isotopes of interest 16, theorganic phase 6′ may be extracted on a continuous basis with a fixedvolume of the second aqueous phase 14. For instance, the organic phase6′ may be substantially continuously contacted with the second aqueousphase 14. The daughter isotopes of interest 16 may have high extractiondistributions into the second aqueous phase 14. As such, the secondaqueous phase 14 may become enriched in the daughter isotopes ofinterest 16 while the organic phase 6′ is depleted of the daughterisotopes of interest 16. The organic phase 6′ may be continuouslyextracted with the second aqueous phase 14 until a sufficient loading ofthe daughter isotopes of interest 16 is obtained in the second aqueousphase 14 to produce a daughter isotope loaded second aqueous phase 14′.Alternatively, once the organic phase 6 is sufficiently enriched orloaded with the parent isotopes (becoming the organic phase 6′), theorganic phase 6′ may be extracted on a continuous basis with the secondaqueous phase 14 in the same vessel.

The second aqueous phase 14 may be an acidic solution, such as a nitricacid solution. The nitric acid solution may have a nitric acidconcentration ranging from approximately 2M to approximately 6M, such asfrom approximately 3M to approximately 5M. The acidity of the secondaqueous phase 14 may be adjusted to achieve optimal distribution of thedaughter isotopes of interest 16 into the second aqueous phase 14 whilethe parent isotopes remain in the organic phase 6′.

In order to substantially continuously respectively contact the organicphase 6 with the first aqueous phase 2 or the organic phase 6′ with thesecond aqueous phase 14, each of the vessels in which the liquid-liquidextraction is performed may be an annular centrifugal contactor (“ACC”).In other words, a first ACC may be used as the first vessel 4 tosubstantially continuously contact the organic phase 6 and the firstaqueous phase 2. In addition, a plurality of ACC's that are configuredin series may be utilized to achieve sufficient loading of the organicphase 6 with the parent isotopes. Once the organic phase 6 issufficiently enriched or loaded with the parent isotopes, contact may bestopped between the first aqueous phase 2 and the organic phase 6. Thefirst aqueous phase 2 and the organic phase 6′ may then be separated.The first ACC may also be used to separate the parent isotope loadedorganic phase 6′ from the first aqueous phase 2. The same ACC, i.e., thefirst ACC, may then be utilized as the second vessel 8 to substantiallycontinuously contact the organic phase 6′ with second aqueous phase(s)14. Alternatively, a second ACC may be used as the second vessel 8 tosubstantially continuously contact the parent isotope loaded organicphase 6′ and the second aqueous phase 14. The second vessel 8 may alsobe used to separate the organic phase 6′ from the daughter isotopeloaded second aqueous phase 14′.

The ACC is known as a “contactor” because it enables the organic phasesand the aqueous phases to be brought into intimate contact with oneanother. ACCs are commercially available, such as from CostnerIndustries Texas LP (Houston, Tex.), and provide a high throughputmethod of performing the liquid-liquid extraction. The ACC is configuredto be able to substantially continuously contact organic phases andaqueous phases and to be able to mix and separate the organic andaqueous phases in a single device. As such, the ACC may enable theprocess of the present invention to be automated and utilize very littleoperator involvement. Examples of ACCs include those described in U.S.Pat. Nos. 5,571,070 and 5,591,340 to Meikrantz et al. and U.S. Pat. No.4,959,158 to Meikrantz, the disclosures of each of which areincorporated by reference herein. As shown in FIG. 4, the organic phase6 and the first aqueous phase 2 may be introduced into the ACC 20through inlet ports 22, 22′. The organic phase 6 and the first aqueousphase 2 may be separately introduced through the inlet ports 22, 22′ ormay be introduced as a mixed phase through the inlet ports 22, 22′. Theorganic phase 6 and the first aqueous phase 2 are introduced to a mixingzone of the ACC 20 and migrate downward to a floor of housing 24 of theACC 20. Radial vanes 26 direct the organic phase 6 and the first aqueousphase 2 into an interior of a hollow rotor 28. Centrifugal force ofrotation of the hollow rotor 28 forces the more dense phase, typicallythe aqueous phase, outward against a wall of the hollow rotor 28. Theless dense phase, typically the organic phase, is displaced radiallyinwardly towards a shaft 30 of the hollow rotor 28. The organic phase 6flows over weir 36 and is collected in a channel from which it exits theACC 20 at outlet port 38. The first aqueous phase 2 flows over weir 32and into a collector, from which it exits at outlet port 34. Afterexiting the ACC 20, each of the organic phase 6 or the first aqueousphase 2 may be reintroduced into the ACC 20 to enable the organic phaseand the first aqueous phase 2 to be substantially continuously contactedwith one another. Alternatively, the organic phase 6′ may be collectedif sufficient loading of the parent isotopes has been achieved. Whilethe flow of the organic phase 6 and the first aqueous phase 2 throughthe ACC 20 has been described in detail herein, a similar manner may beused to flow the organic phase 6′ and the second aqueous phase 14through the ACC 20 and collect daughter isotope loaded second aqueousphase 14′.

Depending on the stage of the liquid-liquid extraction process, an ACC20 may be operated until sufficient loading of the parent isotope isobtained in the organic phase 6 to result in parent isotope loadedorganic phase 6′ or until sufficient loading of the daughter isotopes ofinterest 16 is obtained in the second aqueous phase 14 to result indaughter isotope loaded second aqueous phase 14′. The ACC 20 may be usedto separate the organic phase 6′ enriched in the parent isotopes fromthe first aqueous phase 2 or may be used to separate the second aqueousphase 14′ enriched in the daughter isotopes of interest 16 from theorganic phase 6′.

The second aqueous phase 14′, into which the daughter isotopes ofinterest 16 are extracted, may be periodically taken offline or removedfrom the liquid-liquid extraction system 12, such as when sufficientloading of the daughter isotopes of interest 16 in the second aqueousphase 14′ is achieved. To achieve the sufficient loading, the continuousextraction of the organic phase 6′ with the second aqueous phase 14 maybe performed for at least approximately 30 days and up to a maximum ofapproximately 100 days. The second aqueous phase 14′ may be replacedwith an equal volume of a third aqueous phase (not shown) in theliquid-liquid extraction system 12. The third aqueous phase may be insubstantially continuous contact with the organic phase 6′ to continueextracting additional daughter isotopes of interest 16 from the organicphase 6′ while the second aqueous phase 14′ is processed to recover thedaughter isotopes of interest 16, as described below. The third aqueousphase may be an acidic solution, such as an acidic solution similar tothat used as the second aqueous phase 14. After the daughter isotopes ofinterest 16 have been removed from the second aqueous phase 14′, thethird aqueous phase may be taken offline and processed to remove thedaughter isotopes of interest 16 while the second aqueous phase 14′,which is now depleted of the daughter isotopes of interest 16, may beused in the liquid-liquid extraction system 12.

In one embodiment, the organic phase 6′ is transferred from the storagetank 40 to the second vessel 8, as shown in FIG. 3. The storage tank 40may hold a volume of approximately 210,000 L of the organic phase 6′,which may include the parent isotopes, 73,000 kg of 1M DA[AP], andIsopar L. The organic phase 6′ may be substantially continuouslycontacted with the second aqueous phase 14 to extract the daughterisotopes of interest 16 into the second aqueous phase 14, producing thesecond aqueous phase 14′, which is enriched in the daughter isotopes ofinterest 16. For the sake of example only, the second vessel 8 may be a41 cm ACC having a throughput of approximately 175 L/min. As previouslydescribed, the second aqueous phase 14 may be a nitric acid solutionhaving a nitric acid concentration of 3M. The second aqueous phase 14may be stored in storage tank 40′. The storage tank 40′ may hold avolume of approximately 300 L of the second aqueous phase 14. After theextraction, the organic phase 6′ is depleted of the daughter isotopes ofinterest, becoming organic phase 6″, which may be recirculated to thestorage tank 40. The parent isotopes in the organic phase 6″ may furtherdecay into the daughter isotopes of interest, which may be extracted ina similar manner. The second aqueous phase 14′ enriched in the daughterisotopes of interest 16 may be processed by chromatographic techniques,as described below. The second aqueous phase 14′ may also include smallamounts of the parent isotopes (Th-232 and U-233), radium-224(“Ra-224”), radium-228 (“Ra-228”), and stable metal ion impurities.

Before recovering the daughter isotopes of interest 16, tramp organicsmay be removed from the second aqueous phase 14′. The tramp organics areresidues of dissolved and dispersed solvents, such as hydrocarbonsolvents, and extractant degradation products that are used or found inthe organic phase 6. During the extraction process, small amounts of thehydrocarbon solvents may undesirably be extracted into the secondaqueous phase 14′. The tramp organics may be removed from the secondaqueous phase 14′ using the Argonne Alcohol Extraction (“ARALEX”)process. The ARALEX process is an extraction process that utilizes animmiscible alcohol, such as 2-ethyl-1-hexanol, to remove the residualhydrocarbon solvents from the second aqueous phase 14′. Removal of thetramp organics may enable better separation performance of the secondaqueous phase 14′ on separation column 10 when recovering the daughterisotopes of interest 16. Removal of the tramp organics may also protectsubsequent separation columns 10 from degradation and overloading.

The second aqueous phase 14′, which is enriched in the daughter isotopesof interest 16, may be processed by a variety of chromatographictechniques to remove, purify, and concentrate the daughter isotopes ofinterest 16. The second aqueous phase 14′ may also be processed toremove minor amounts of the parent isotopes that remain in the secondaqueous phase 14′ and other undesired compounds, such as undesireddaughter isotopes. The chromatographic techniques may include ionexchange chromatography, such as cation exchange chromatography or anionexchange chromatography, and extraction chromatography. Resins that maybe used include, but are not limited to, DOWEX® 1X8 resin, which isavailable from Dow Corning Corp., (Michigan, U.S.A.); TEVA™ resin, whichis a tetravalent actinide resin having a quaternary ammonium salt (amixture of trioctyl and tridecyl methyl ammonium chlorides) sorbed on awater-insoluble support and is available from Eichrom Industries, Inc.(Darien, Ill.); Dipex® resin, which has diphosphonic acid (“DPA”) groupssorbed onto an inert substrate and is available from Eichrom Industries;Diphosil™ resin, which is available from Eichrom Industries; Diphonix®resin, which is available from Eichrom Industries; UTEVA® or UTEVA®-2resin, which has DA[AP] as the extractant and a TRPO sorbed ontosilanized silica and is available from Eichrom Industries; adiglycolamide (“DGA”) resin having a tetraalkyldiglycolamide as theextractant that is coated on inert support particles; and2-ethylhexyl-2-ethylhexylphosphonic acid on an inert substrate. Each ofthese resins may be packed into a column , such as separation column 10.

For instance, a DGA resin may be used to remove the daughter isotopes ofinterest 16, such as Ac-225, from the second aqueous phase 14′. The DGAresin may include a tetraalkyldiglycolamide, such asN,N,N′,N′-tetra-N-alkyl-3-oxopentanediamide (“TN-DGA”),N,N,N′,N′-tetra-n-octyl diglycolamide (“TO-DGA”), the branched alkylN,N,N′,N′-tetra-(2-ethyl hexyl)-3-oxopentanediamide (“TB-DGA”), othertetraalkyldiglycolamides, or mixtures thereof, which is coated on inertsupport particles. The DGA resin may be a TO-DGA resin or a TB-DGAresin, which are each available from Eichrom Industries. The inert,porous support may include polymeric resins or silica particles. Whenthe second aqueous phase 14′ contacts the DGA resin, the Ac-225 may besorbed to the DGA resin while the parent isotopes or the undesireddaughter isotopes, such as Ra-224 or Ra-225, elute from the DGA resin.The daughter isotopes of interest 16 may subsequently be eluted from theDGA resin by contacting the DGA resin with water, dilute (less thanapproximately 0.1 M) hydrochloric acid, or dilute (less thanapproximately 0.1 M) nitric acid.

The second aqueous phase 14′ may be flowed through the separation column10 that is packed with the ion exchange resin or the extraction resin.The separation column 10 may bind the daughter isotopes of interest 16while allowing the parent isotopes or the undesired daughter isotopes toelute. For instance, a DGA column may be used to bind the Ac-225 whileother components of the second aqueous phase 2′ elute. Alternatively,the separation column 10 may bind the parent isotopes or the undesireddaughter isotopes while allowing the daughter isotopes of interest 16 toelute. For instance, trace amounts of the U and Th parent isotopesremaining in the second aqueous phase 14′ may be removed by passing thesecond aqueous phase 14′ through an extraction column that binds the Uand Th parent isotopes while the Ac-225 elutes. The extraction columnmay be a UTEVA®-2 resin. Similarly, if the second aqueous phase 14′includes undesired daughter radioisotopes, such as Ra-225, the secondaqueous phase 14′ may be passed through an ion exchange column to bindthe Ac-225 while the Ra-225 elutes. The Ra-225 that elutes may becollected and stored for a sufficient amount of time to decay to Ac-225,at which time the Ac-225 may be processed as previously described.Various combinations of chromatographic techniques, such as usingdifferent types of chromatographic resins, may be used to purify andconcentrate the Ac-225.

Each of the above-described resins may be packed into separation columns10, as known in the art. Chromatographic conditions, such as flow ratesand mobile phases, used to separate the daughter isotopes of interest 16from the second aqueous phase 14′ may be selected by one of ordinaryskill in the art and, as such, are not discussed in detail herein.

In one embodiment, the daughter isotopes of interest 16 may be removed,purified, and concentrated from the second aqueous phase 14′ by passingthe second aqueous phase 14′ through various separation columns 10.However, before purifying the second aqueous phase 14′, the tramporganics may be removed by introducing the second aqueous phase 14′ intoa contactor, such as ACC 50, as shown in FIG. 5. The ACC 50 may be a 5cm or 12.5 cm ACC. The tramp organics may be removed using the ARALEXprocess, as previously described. Second aqueous phase 14″ exiting fromthe ACC 50 may be substantially free of tramp organics. The secondaqueous phase 14″ may be passed through separation column 10′, which ispacked with the UTEVA® or the UTEVA®-2 resin. The separation column 10′may have a bed volume ranging from approximately 1 L to approximately 2L. The separation column 10′ may bind the U and Th parent isotopes whilethe daughter isotopes of interest 16, such as the Ac-225, elute. In oneembodiment, the UTEVA®-2 resin is used in the separation column 10′because the UTEVA®-2 resin is able to remove more parent isotopes thanthe UTEVA® resin. The daughter isotopes of interest 16 may then bepassed through separation column 10″, which is packed with the DGAresin. The separation column 10″ may have a bed volume of approximately100 ml. The daughter isotopes of interest 16 may bind to the DGA resinin the separation column 10″ while undesired daughter isotopes 52, suchas Ra-224 or Ra-225, elute. To elute the daughter isotopes of interest16 from the separation column 10″, a 0.1M HNO₃ solution may be passedthrough the separation column 10″. The daughter isotopes of interest 16may elute in a smaller volume, such as approximately 100 ml. To furtherreduce the volume in which the recovered daughter isotopes of interest16 are present, the recovered daughter isotopes of interest 16 may beprocessed through small separation columns 10′,10″ loaded with UTEVA®resin, UTEVA®-2 resin, or DGA resin. These separation columns 10′,10″may each have a bed volume of approximately 10 ml.

The volume of the second aqueous phase 14′ may be processed through theseparations columns 10 at one time or may be processed batchwise. Afterthe volume of the second aqueous phase 2′ has been processed, thedaughter isotopes of interest 16 may be recovered from the separationcolumn 10. For instance, if the daughter isotopes of interest 16 arebound to the separation column 10, the daughter isotopes of interest 16may be eluted using an acidic solution, such as a nitric acid orhydrochloric acid solution, and collected. The acidic solution may havean acid concentration that ranges from approximately 0.001 M toapproximately 6 M. In one embodiment, the daughter isotopes of interest16 are stripped from the DGA column using 0.1 M nitric acid. Thedaughter isotopes of interest 16 that are collected from the separationcolumn 10 may then be shipped to a customer. Alternatively, the daughterisotopes of interest 16 may be retained on the separation column 10,which serves as a storage vessel until the daughter isotopes of interest16 are to be used. The separation column 10 may also function as ashipping vessel in which the daughter isotopes of interest 16 retainedon the separation column 10 are delivered to the customer. The daughterisotopes of interest 16 may be stripped from the separation column 10 bythe customer.

After elution from the separation column 10, additional purification andconcentration steps may be performed to further purify and concentratethe daughter isotopes of interest 16. For instance, the nitric acidconcentration of the solution including the daughter isotopes ofinterest 16 may be adjusted to approximately 3 M. This solution may thenbe reprocessed through the UTEVA®-2 column and the DGA column, aspreviously described.

By utilizing the method of the present invention, convenient andefficient recovery of the daughter isotopes of interest 16 may beachieved. The liquid-liquid extraction system 12 described herein mayhave a recovery efficiency of at least approximately 90%. In contrast,the precipitation process described in Tranter has a recovery efficiencyof approximately 40% to approximately 60%. Since the daughter isotopesof interest 16 are continuously removed from the organic phase 6′, theorganic phase 6′ is not stored to allow the parent isotopes to decaybefore performing the liquid-liquid extraction. In addition, bycontinuously removing the daughter isotopes of interest 16, theradiation dose on the organic phase 6′ may be reduced, which increasesthe stability of the organic phase 6′. Furthermore, the liquid-liquidextraction may be repeated numerous times as the daughter isotopes ofinterest 16 decay from the long-lived parent isotopes. Since the parentisotopes continually generate decay products that include the daughterisotopes of interest 16, the organic phase 6′ may be contacted with thesecond aqueous phase 14 on a continuous basis to extract the daughterisotopes of interest 16. In addition, since the U-233 is not separatedfrom the thorium isotopes during the liquid-liquid extraction, continueddecay of the U-233 produces additional quantities of Th-229 that areavailable as the parent isotopes. Furthermore, no additional safeguardissues are raised with the method of the present invention.

Since the daughter isotopes of interest 16 that are eluted from theseparation column 10 include Ac-225, the method of the present inventionmay provide a sufficient supply of Ac-225 for use in labeling monoclonalantibodies. Additionally, since the Ac-225 decays to Bi-213, the Ac-225may be used as a parent isotope of Bi-213, providing a sufficient supplyof Bi-213 for use in labeling monoclonal antibodies. Since Bi-213 has ashort half-life, the Bi-213 may be quickly extracted from the Ac-225source and administered to a patient.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A method of recovering at least one daughter isotope from aradioisotope mixture, comprising: providing a radioisotope mixturesolution comprising at least one parent isotope; extracting the at leastone parent isotope into an organic phase; substantially continuouslycontacting the organic phase with an aqueous phase; substantiallycontinuously extracting at least one daughter isotope into the aqueousphase; and purifying the at least one daughter isotope from the aqueousphase.
 2. The method of claim 1, wherein providing the radioisotopemixture solution comprising the at least one parent isotope comprisesproviding an acidic solution comprising uranium and thorium.
 3. Themethod of claim 1, wherein providing the radioisotope mixture solutioncomprising the at least one parent isotope comprises providing theradioisotope mixture solution comprising uranium and thorium and havinga nitric acid concentration ranging from approximately 2 M toapproximately 6 M.
 4. The method of claim 1, wherein providing theradioisotope mixture solution comprising the at least one parent isotopecomprises providing the radioisotope mixture solution comprising uraniumand thorium and having a nitric acid concentration ranging fromapproximately 3 M to approximately 5 M.
 5. The method of claim 1,wherein providing the radioisotope mixture solution comprising the atleast one parent isotope comprises providing a breeder reactor fuel thatcomprises uranium and thorium.
 6. The method of claim 1, whereinproviding the radioisotope mixture solution comprising the at least oneparent isotope comprises providing a breeder reactor fuel that comprisesat least one of uranium-232, uranium-233, thorium-228, thorium-229,thorium-232, and mixtures thereof.
 7. The method of claim 1, whereinextracting the at least one parent isotope into the organic phasecomprises extracting the at least one parent isotope into the organicphase using an annular centrifugal contactor.
 8. The method of claim 1,wherein extracting the at least one parent isotope into the organicphase comprises extracting the at least one parent isotope into theorganic phase that comprises an extractant selected from the groupconsisting of n-tributyl phosphate, dibutyl phosphate,di-n-amyl-n-amylphosphonate, dibutyl butyl phosphonate, butyl dibutylphosphinate, dibutyl cyclohexyl phosphonate, dibutyl chloromethylphosphonate, tri(4-methylpentyl-2)phosphate, butyl phosphonate,di(4-methylpentyl-2)butyl phosphonate, di(4-methylpentyl-2)isobutylphosphonate, di(4-methylpentyl-2)propyl phosphonate, anddi(2-ethylbutyl)2-ethylbutyl phosphonate.
 9. The method of claim 1,wherein extracting the at least one parent isotope into the organicphase comprises extracting the at least one parent isotope into theorganic phase that comprises an extractant present from approximately0.5 M to approximately 2.0 M.
 10. The method of claim 1, whereinextracting the at least one parent isotope into the organic phasecomprises extracting the at least one parent isotope into the organicphase that comprises a solvent selected from the group consisting ofbenzene, carbon tetrachloride, isopropyl ether, 1-octanol, 2-ethylhexanol, 1-decanol, 1-octanoic acid, methyl isobutylketone,p-diisopropylbenzene, dodecane, n-heptane, a normal paraffinichydrocarbon solvent, an isoparaffinic hydrocarbon solvent, and kerosene.11. The method of claim 1, wherein substantially continuously contactingthe organic phase with the aqueous phase comprises substantiallycontinuously contacting the organic phase with the aqueous phase thatcomprises from approximately 2 M to approximately 6 M nitric acid. 12.The method of claim 1, wherein substantially continuously contacting theorganic phase with the aqueous phase comprises substantiallycontinuously contacting the organic phase with the aqueous phase thatcomprises from approximately 3 M to approximately 5 M nitric acid. 13.The method of claim 1, wherein substantially continuously extracting theat least one daughter isotope into the aqueous phase comprisessubstantially continuously extracting the at least one daughter isotopeinto the aqueous phase using an annular centrifugal contactor.
 14. Themethod of claim 1, wherein purifying the at least one daughter isotopefrom the aqueous phase comprises purifying the at least one daughterisotope by ion exchange chromatography or extraction chromatography. 15.The method of claim 1, wherein purifying the at least one daughterisotope from the aqueous phase comprises purifying at least one ofactinium-225, radium-225, and mixtures thereof from the first aqueousphase.
 16. The method of claim 1, wherein purifying the at least onedaughter isotope from the aqueous phase comprises removing the aqueousphase from a liquid-liquid extraction system and replacing the aqueousphase in the liquid-liquid extraction system with another aqueous phase.17. The method of claim 1, wherein purifying the at least one daughterisotope from the aqueous phase comprises removing tramp organics fromthe aqueous phase by extracting the tramp organics with an immisciblealcohol.
 18. The method of claim 1, wherein purifying the at least onedaughter isotope from the aqueous phase comprises sorbing actinium-225onto a diglycolamide resin, wherein the diglycolamide resin comprises atetraalkyldiglycolamide extractant coated on inert support particles.19. The method of claim 18, wherein sorbing actinium-225 onto thediglycolamide resin comprises sorbing the actinium-225 onto thediglycolamide resin comprisingN,N,N′,N′-tetra-N-alkyl-3-oxopentanediamide, N,N,N′,N′-tetra-n-octyldiglycolamide, N,N,N′,N′-tetra-(2-ethyl hexyl)-3-oxopentanediamide, ormixtures thereof as the tetraalkyldiglycolamide extractant.
 20. Themethod of claim 1, further comprising recovering the at least onedaughter isotope from the aqueous phase.
 21. The method of claim 1,further comprising enabling the at least one daughter isotope to decayto at least one subsequent daughter isotope and recovering the at leastone subsequent daughter isotope.
 22. The method of claim 1, furthercomprising enabling actinium-225 to decay to bismuth-213 and recoveringthe bismuth-213.
 23. A method of recovering at least one daughterisotope from a radioisotope mixture, comprising: providing aradioisotope mixture solution comprising at least one parent isotope;contacting the radioisotope mixture solution with an organic phase;extracting the at least one parent isotope into the organic phase;separating the organic phase enriched in the at least one parent isotopefrom the radioisotope mixture solution depleted in the at least oneparent isotope; substantially continuously contacting the organic phaseenriched in the at least one parent isotope with an aqueous phase;substantially continuously extracting at least one daughter isotope intothe aqueous phase; separating the organic phase enriched in the at leastone parent isotope from the aqueous phase enriched in the at least onedaughter isotope; and purifying the at least one daughter isotope fromthe aqueous phase.
 24. The method of claim 23, wherein providing theradioisotope mixture solution comprising the at least one parent isotopecomprises providing the radioisotope mixture solution comprising uraniumand thorium.
 25. The method of claim 23, wherein providing theradioisotope mixture solution comprising the at least one parent isotopecomprises providing an acidic solution comprising uranium and thoriumand having a nitric acid concentration ranging from approximately 2 M toapproximately 6 M.
 26. The method of claim 23, wherein providing theradioisotope mixture solution comprising the at least one parent isotopecomprises providing an acidic solution comprising uranium and thoriumand having a nitric acid concentration ranging from approximately 3 M toapproximately 5 M.
 27. The method of claim 23, wherein providing theradioisotope mixture solution comprising the at least one parent isotopecomprises providing a breeder reactor fuel that comprises uranium andthorium.
 28. The method of claim 23, wherein providing the radioisotopemixture solution comprising at least one parent isotope comprisesproviding a breeder reactor fuel that comprises at least one ofuranium-232, uranium-233, thorium-228, thorium-229, thorium-232, andmixtures thereof.
 29. The method of claim 23, wherein extracting the atleast one parent isotope into the organic phase comprises extracting theat least one parent isotope into the organic phase using an annularcentrifugal contactor.
 30. The method of claim 23, wherein extractingthe at least one parent isotope into the organic phase comprisesextracting the at least one parent isotope into the organic phase thatcomprises an extractant selected from the group consisting of n-tributylphosphate, dibutyl phosphate, di-n-amyl-n-amylphosphonate, dibutyl butylphosphonate, butyl dibutyl phosphinate, dibutyl cyclohexyl phosphonate,dibutyl chloromethyl phosphonate, tri(4-methylpentyl-2) phosphate, butylphosphonate, di(4-methylpentyl-2)butyl phosphonate,di(4-methylpentyl-2)isobutyl phosphonate, di(4-methylpentyl-2)propylphosphonate, and di(2-ethylbutyl)2-ethylbutyl phosphonate.
 31. Themethod of claim 23, wherein extracting the at least one parent isotopeinto the organic phase comprises extracting the at least one parentisotope into the organic phase that comprises an extractant present fromapproximately 0.5 M to approximately 2.0 M.
 32. The method of claim 23,wherein extracting the at least one parent isotope into the organicphase comprises extracting the at least one parent isotope into theorganic phase that comprises a solvent selected from the groupconsisting of benzene, carbon tetrachloride, isopropyl ether, 1-octanol,2-ethyl hexanol, 1-decanol, 1-octanoic acid, methyl isobutylketone,p-diisopropylbenzene, dodecane, n-heptane, a normal paraffinichydrocarbon solvent, an isoparaffinic hydrocarbon solvent, and kerosene.33. The method of claim 23, wherein substantially continuouslycontacting the organic phase enriched in the at least one parent isotopewith the aqueous phase comprises substantially continuously contactingthe organic phase with the aqueous phase that comprises fromapproximately 2 M to approximately 6 M nitric acid.
 34. The method ofclaim 23, wherein substantially continuously contacting the organicphase enriched in the at least one parent isotope with the aqueous phasecomprises substantially continuously contacting the organic phase withthe aqueous phase that comprises from approximately 3 M to approximately5 M nitric acid.
 35. The method of claim 23, wherein substantiallycontinuously extracting the at least one daughter isotope into theaqueous phase comprises substantially continuously extracting the atleast one daughter isotope into the aqueous phase using an annularcentrifugal contactor.
 36. The method of claim 23, wherein purifying theat least one daughter isotope from the aqueous phase comprises purifyingthe at least one daughter isotope by ion exchange chromatography orextraction chromatography.
 37. The method of claim 23, wherein purifyingthe at least one daughter isotope from the aqueous phase comprisespurifying at least one of actinium-225, radium-225, and mixtures thereoffrom the first aqueous phase.
 38. The method of claim 23, whereinpurifying the at least one daughter isotope from the aqueous phasecomprises removing tramp organics from the aqueous phase by extractingthe tramp organics with an immiscible alcohol.
 39. The method of claim23, wherein purifying the at least one daughter isotope from the aqueousphase comprises sorbing actinium-225 onto a diglycolamide resin, whereinthe diglycolamide resin comprises a tetraalkyldiglycolamide extractantcoated on inert support particles.
 40. The method of claim 39, whereinsorbing actinium-225 onto the diglycolamide resin comprises sorbing theactinium-225 onto the diglycolamide resin comprisingN,N,N′,N′-tetra-N-alkyl-3-oxopentanediamide, N,N,N′,N′-tetra-n-octyldiglycolamide, N,N,N′,N′-tetra-(2-ethyl hexyl)-3-oxopentanediamide, ormixtures thereof as the tetraalkyldiglycolamide extractant.
 41. Themethod of claim 23, wherein purifying the at least one daughter isotopefrom the aqueous phase comprises removing the first aqueous phase from aliquid-liquid extraction system and replacing the aqueous phase in theliquid-liquid extraction system with another aqueous phase.
 42. Themethod of claim 23, further comprising enabling the at least onedaughter isotope to decay to at least one subsequent daughter isotopeand recovering the at least one subsequent daughter isotope.
 43. Themethod of claim 23, further comprising enabling actinium-225 to decay tobismuth-213 and recovering the bismuth-213.